fix(StockService): 修复MES成功判断逻辑 - 检查Data.IsSuccess而非HTTP层IsSuccess

HttpResponseResult<MesResponse>有两个IsSuccess:
- HttpResponseResult.IsSuccess: HTTP层成功(网络层面)
- mesResult.Data.IsSuccess: MES业务层成功(Code==0)

修复前错误地检查HTTP层，HTTP 200但MES返回错误码时误认为成功。

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>